Waveguide switching structure having at least one bulb filled with a low pressure gas



Ju 6, 1967 B. BLACHIER ETAL 3,

WAVEGUIDE SWITCHING STRUCTURE HAVING AT LEAST ONE BULB FILLED WITH A LOW PRESSURE GAS Filed April 29, 1964 4 Sheets-Sheet 1 LOW PRESSURE June 6. 1 7 B. BLACHIER ETAL 3,324,420

WAVEGUIDE SWITCHING STRUCTURE HAVING AT LEAST ONE BULB FILLED WITH A LOW PRESSURE GAS Filed April 29, 1964 4 Sheets-Sheet 2 Fig.3 I07 I l80 PHASE SH/F TERS MAG/C TEE 11 r02 5 Hg. 4

"\souARE a a WAVE VOLTAGE GENERATOR 10/ a 90 PHASE SHIFTER 3dB HYBRID 90PHA$E SHIFTER J l b F7 M U0 9 co I O bb. t

J n 6. 19 B. BLACHIER ETAL 3,324,420

WAVEGUIDE SWITCHING STRUCTURE HAVING AT LEAST ONE BULB FILLED WITH A LOW PRESSURE GAS Filed April 29, 1964 4 Sheets-Sheet 3 2&7 s05 Fig.6 '5 423 l '5 f k 2 504 20 Fig. 7 2 5 J n 6. 1967 B. BLACHIER ETAL 3,324,420

WAVEGUIDE SWITCHING STRUCTURE HAVING AT LEAST ONE BULB FILLED WITH A LOW PRESSURE GAS Filed April'29, 1964 4 Sheets-Sheet 4 United States Patent O WAVEGUEDE SW1"! CHING STRUCTURE HAVING AT LEAST GNE BULB FTLLED WITH A LOW PRESSURE GAS Bruno Blachier and NGuyen Van Tran, Paris, France, assignors to CSF-(Iompagnie Generale d'e Telegraphic Sans Fil, a corporation of France Filed Apr. 29, 1964, Ser. No. 363,484 Claims priority, application France, May 3, 1963, 933,97 7 Claims. (Cl. 333-7) The present invention relates to microwave switching or commutating techniques.

The problem of switching microwave energy between two channels is often encountered in radar and radio links techniques, in particular where waveguides are used.

In many cases, an extremely rapid commutation of substantial energy amounts is desired. This is, in particular, true for radar systems.

Many systems have been proposed to this end, and among them the ferrite switches. However, ferrite switches are generally not stable because of the losses due to temperature increases when high energy amounts are involved. Besides, substantial energy is required for controlling such switches.

Y junctions, whose branches include resonators, within which plasma is created by means of an external voltage are also known. This plasma detunes the resonator and thus modifies the transfer characteristics.

However, such plasma switches have substantial drawbacks:

(a) The passband is limited by the high Q factor of the resonators.

(b) The adjustment of the rate of ionization of the plasma sets difiicult problems. If it is too high, the microwave field may, by itself, initiate the formation of plasma, without any control voltage being applied, this being due to the ultra-high frequency energy concentration in the resonator.

(c) If the rate of ionization is too low, the detuning upon plasma formation may be too low.

It is an object of this invention to provide a microwave plasma switch free from such troubles. In the plasma switch of the invention, the gas, which is ionized into plasma, is at a very low pressure, say of order of 0.1 mm. Hg, so that no ionization is possible under the action of the ultra-high frequency field alone. Besides, the housing in which plasma is formed is placed where the microwave field intensity is low and the formation of plasma modifies to an appreciable degree the electromagnetic field outside of the area where it is created by means of a low frequency control voltage.

The wave that propagates through the area, where plasma is for-med, may be, for example, a travelling wave.

The invention will be better understood from the following specification and appended drawings wherein:

FIGS. 1 and 2 show in perspective phase shifting structures to form microwave switches according to the invention;

FIGS. 3 and 4 are diagrammatic views of switches according to the invention;

FIG. 5 is an explanatory diagram; and

FIGS. 6 to 10 show further embodiments of the invention.

3,324,42fi Patented June 6, 1967 Referring to FIG. 1, there is shown a rectangular waveguide 1, within which a travelling Wave propagates. Along one of the small sides of guide 1 is placed a curved bulb 2, for example of glass, filled With a very low pressure gas, for example 10- Torr.

At the ends of bulb 2 are respectively placed electrodes 3 and 4, between which an A.-C. supply 5 establishes a low frequency sinusoidal field at predetermined instants.

The unit operates as follows:

A high energy wave propagates along the guide. The gas within bulb 2 being at a low pressure, this energy cannot by itself initiate plasma formation. As long as said gas is not ionized, bulb 2 does not have any appreciable effect on wave propagation, its reactive impedance being low.

When A.-C. voltage is applied to electrodes 3 and 4, the gas is ionized into plasma and becomes conductive. It is then as though the guide side wall were moved to match the inner wall of bulb 2. This brings about an additional phase-shift in the wave propagation along guide 1. Thus, when no voltage is applied to electrodes 3 and 4, bulb 2 behaves as a good dielectric. During the time intervals when voltage is applied to electrodes 3 and 4, the plasma filled bulb 2 behaves as a perfect reflector. The effect is the same as if the waveguide wall were set off by a maximum distance Aa.

The phase-shift thus brought about can be expressed as:

where Aa represents the above mentioned guide wall transversal displacement,

the wave number in free space, and a is the width of the guide.

To obtain a phase shift Ag0=1r, taking A as unity and writing:

If it is desired that the phase shifting structure may operate w1thin a 10% frequency band, one may take a cut oil? wavelength A =2a= 1.15 t

For

and since the above formula gives: l=1.5)\

FIG. 2 shows a further embodiment of the invention. Instead of bulb 2 of FIG. 1, a plurality of tubes 21 are inserted along the waveguide lateral wall. Electrodes 30 and 40 are provided at the upper and lower ends of tubes 21.

The entire length of the waveguide portion, where phase shifting elements 21 are placed, is, for example, 15k the number of bulbs being for example about 40. The bulbs are equispaced and fed in parallel, each of them furnishing a phaseshift of the order of 10%. The total phaseshift is of the order of 360.

The switch shown in FIG. 3 comprises two phaseshifters 101 and 102 according to the invention.

Phaseshifters 101 and 102 are placed in branches I and II of a magic tee 4, having output branches III and IV. According to whether they are excited or not, phaseshifters 101 and 102 provide a 1: or O phaseshift. The structure being symmetrical, the propagations through the two channels are either in phase or 180 out of phase. As is well known, the output energy flows through branch III or branch IV as the case may be.

FIG. 4 shows a further switch. Phascshifters 101 and 102 are placed in the two input arms 1a and 1b of a 3 db hybrid junction J. the control inputs an and bi) of phaseshifters 101 and 102 are coupled to a square wave voltage generator, which provides at its outputs, at aa and bb respectively, the waves shown in FIG. 5. These waveforms have a period of T and are out of phase by T/2. The maximum voltage U is adjusted so that each phaseshifter will give a 11'/ 2 phaseshift. Under these conditions, when phaseshifter 101 is energized, energy is collected at the output arm 23. When phaseshifter 102 is energized, energy is collected at the output arm 22.

The arrangement has the following advantages:

(a) Phaseshifts by only 1r/ 2 may be used, which involves lower losses; (b) The arrangement is perfectly symmetrical.

The losses are negligible compared to the switching coeificient (fraction of the energy appearing in the arm when no energy is wanted).

FIGS. 6, 7 and 8 show further embodiments of the invention.

In the switch portion of FIG. 6, the bulb has a rectangular cross section. The two broad walls 201 and 202 having a convex cylindrical shape extending within the waveguide. Upper and lower Walls 203 and 204 are metallized and control electrodes 303 and 304 are soldered thereto.

In the embodiment of FIG. 7, the phaseshifting bulb is identical to that of FIG. 6, but guide 1 has in wall 10, facing the bulb, a bulge, the maximum lateral dimension of which is A, This arrangement results in that the loss is the same, whether the bulb is triggered, or not.

In the switch portion shown in FIG. 8 two enclosures 20 and 21 are provided all along the adjacent walls 10 and 11 of guide 1. Enclosures and 21 are controlled by four electrodes 303, 304 and 305, 306. The formation of plasma results in a restriction of the useful guide section by A,,/ 2 along each lateral wall.

FIG. 9 is a top view of a still further embodiment. Bulb 2 is identical to that of FIG. 7, for example. However, on the lateral wall 10 is placed a dissipative body 100, which causes an attenuation substantially equal to the attenuation which occurs in the ionized plasma filling tube 2.

FIG. 10 is still another embodiment, incorporating a total coupling hybrid junction. The latter comprises three branches: an input branch 1001 and two output branches 1002 and 1003.

Enough windows 1005 are placed between adjacent branches arms 1002 and 1003 for the whole of the energy to pass, by coupling, from branch 1001 into branch 1003. A plasma tube 1006 of cylindrical shape and symmetrical with respect to the wall common to branches 1002 and 1003, is excited by electrodes 1007 and 1008 connected to an A.-C. power supply.

When this tube is energized, everything happens as though there were no windows, and energy is confined to branch 1002. In the opposite case, as indicated above, there is total coupling and transfer of energy between branches 1002 and 1003.

The A.-C. power source can be of any known type say a Ruhmkorff coil, for example.

The present invention is of course not limited to the arrangements shown, which were given only by way of example. Generally speaking, the invention provides a microwave switch comprising microwave phaseshifters or similar devices incorporating a low pressure gas contain- .ing enclosure, the plasma formation being caused by a low frequency field and resulting in a modification of the electric field outside said enclosure.

What is claimed, is:

1. A phaseshifting structure for a switch for switching microwave energy from one channel to another comprising: at least one rectangular waveguide, having two small sides and two large sides; near one of said small sides, a curved bulb filled with a low pressure gas, said bulb having two ends and extending from one of said small sides; into said guide; two electrodes respectively positioned at said two ends; and means for feeding to said two electrodes a low frequency alternating voltage; said one small side having between said two ends a curved projection towards outside.

2. A phaseshifting structure for a switch for switching ultra-high frequency energy from one channel to another comprising: at least one rectangular waveguide having two small sides, a plurality of equispaced rod shaped containers filled with a low pressure gas against one of said small sides, each of said containers having two ends; respective electrodes positioned at said ends; and means for feeding a low frequency alternating voltage to said two electrodes.

3. A phaseshifting structure for a switch for switching microwave energy from one channel to another comprising: at least one rectangular waveguide having two small sides and two large sides; a bent bulb extending from one of said small sides into said guide and filled with a low pressure gas, said bulb having two conductive surfaces in said large sides respectively, and means for feeding to said conductive surfaces an alternating voltage having a frequency low with respect to the frequency of said microwave energy.

4. A phaseshifting structure for a switch for switching microwave energy from one channel to another comprising: at least one rectangular waveguide having two small sides and two large sides, against each of said small sides, two enclosures filled with a low pressure gas extending parallel thereto from one large side to the other, two electrodes in each of said enclosures, and means for feeding to said electrodes an A.-C. potential having a frequency low with respect to the frequency of said microwave energy.

5. A switch for switching microwave energy from one channel to another, comprising two identical rectangular waveguides, having respectively two large sides and two small sides, one of said small sides being common to said guides, coupling windows equispaced in said common side, a container enclosing said coupling windows, said container being filled with a low pressure gas, two electrodes connected to said containers; and means for feeding to said two electrodes an alternating potential having a frequency low with respect to the frequency of said energy.

6. A switch for switching microwave energy from one References Cited channel to another comprising two Waveguides havin a common input and respective outputs; in each of said UNITED STATES PATENTS guides, outside the region in which the greatest part of 2,577,146 12/ 1951 Norton 315--39 X energy is concentrated, a container filled with a low pres- 5 2,745,072 5/1956 Goldstein et 5 39 sure gas; means for ionizing said gas selectively in at least one of said containers; and a magic tee having two input 3076157 1/1963 Manwarren 315 39 X arms, respectively coupled to said outputs, and two output HERMAN KARL S B ACH Primary Examiner arms.

7. A switch according to claim 6, wherein said ionizing 10 P. L. GENSLER, Assistant Examiner.

means ionize said gas in both containers. 

3. A PHASESHIFTING STRUCTURE FOR A SWITCH FOR SWITCHING MICROWAVE ENERGY FROM ONE CHANNEL TO ANOTHER COMPRISING: AT LEAST ONE RECTANGULAR WAVEGUIDE HAVING TWO SMALL SIDES AND TWO LARGE SIDES; A BENT BULB EXTENDING FROM ONE OF SAID SMALL SIDES INTO SAID GUIDE AND FILLED WITH A LOW PRESSURE GAS, SAID BULB HAVING TWO CONDUCTIVE SURFACES IN SAID LARGE SIDES RESPECTIVELY, AND MEANS FOR FEEDING TO SAID CONDUCTIVE SURFACES AN ALTERNATING VOLTAGE HAVING A FREQUENCY LOW WITH RESPECT TO THE FREQUENCY OF SAID MICROWAVE ENERGY. 